Record-setting 2012 warmth largely confined to North America, western Europe

Most of the rest of the world has seen little change from 2011.

In March, high temperatures over two-thirds of the continental US set numerous records and made it the nation's warmest March on record. April has been no slouch either, as high temperature records have continued to fall. But at the time of our last report, the services that track global temperatures hadn't analyzed the global extent of the warmth. Now that the numbers for March and April are available, it's clear that the rest of the globe generally hasn't shared the US's record heat.

Globally, the current period of warming began back in the 1970s. NASA's GISTEMP tracks the current global temperature against a baseline established by the 1951-1980 average, and it hasn't seen a calendar year below that average since 1976, or a month below it since 1994. The US climate has generally reflected that, with high temperature extremes dominating over the last several decades, as shown below.

Trends in temperature extremes in the continental US show that 2012 has been exceptionally warm.

That said, the US is a relatively small portion of the global land mass, and an even smaller portion of the planet's total surface area. It's entirely possible to have the US experiencing extreme temperatures without the planet as a whole really noticing. And that's what has seemed to have happened this spring. Even as the US has experienced record-breaking extremes, the GISSTEMP index has seen global temperatures that were roughly equivalent to the ones we experienced last year, and well below those of 2010, the warmest year on record.

GISS also offers a mapping tool that lets you identify regional differences in temperature. You can select the time you want to examine and set the baseline to which you're comparing it. By default, the baseline uses the 1951-1980 time period used by the GISSTEMP data. That's not especially useful for comparing recent trends, though; as we noted above, compared to that baseline, the planet as a whole has been consistently warmer in recent years. If you choose this baseline, then the entire globe will look a bit hot.

To give a more relevant view of recent temperatures, we set the baseline to 1990-2005, during which time the current warming trend was in full swing. With that as a baseline, we asked the GISS system to show us how temperatures from this March stacked up around the globe. The results, shown at top, are pretty striking.

Climate models have consistently predicted that greenhouse warming would be disproportionately felt in polar regions, and those predictions have generally been borne out. So, if you ignore the poles, the remaining warming in March falls heavily in two regions: North America and Western Europe. In fact, the majority of the continent is buried under a color that indicates it is at least 8°C above the baseline average—GISS didn't offer any colors for larger anomalies, or it might even look more dramatic. At the same time, however, the plot makes it clear that nothing especially out of the ordinary was going on for the rest of the planet.

Advance the time by a month, and you can see that North America has remained warm, although not quite to the same extreme. Meanwhile, the far west of Europe had cooled off, and the focus of heat had shifted well into Russia. But again, the rest of the globe was a mottled collection of temperatures much closer to the baseline average.

In April, the US cooled down as Russia got hot. Note the maximum temperatures are lower than in the top graphic.

One of the ironies here is that, even though the global temperatures are fairly typical of the last decade, the unusual spring warmth might have an outsized effect on public opinion. People in the US seem to rely on their personal experience (along with the economy) when they formulate their opinion on climate change. In this case, the citizens of the US and Europe personally experienced unusual warmth, and were more likely to have been exposed to anecdotal reports in the mainstream media. So, even though nothing special happened globally, the year so far may be perceived as an indication of a warming planet.

This is almost the exact converse of what happened in 2010, the warmest year on record. In that year, high temperatures were focused in northern Canada, North Africa, and the Middle East. The US experienced decidedly average temperatures, while Europe was slightly cooler.